1. Field
The present invention relates to a process for making spare parts for refiners used for the production of paper.
More particularly, the present invention relates to a process which allows spare parts to be made for refiners for the preparation of paper pulps. The pulp enters them at one end and exits on the other side, passing through a rotary body equipped with bars or in any case having alternating gaps and solid areas (bars, holes, etc. made in mechanical machining processes and made on one or both faces) and a casing equipped with fixed counter-bars. Said alternation of gaps and solid areas is also referred to as the “set of bars”.
The process in accordance with the invention allows a reduction in the times and costs for the production of such spare parts for refiners, also obtaining a high level of precision in the finished product, with the possibility of making spare parts for any refiners on the market, even the older ones with a narrow angle, which in this way could be used to produce very particular papers which currently require more modern refiners.
The present invention may be applied in mechanics applied to the papermaking sector.
2. General Background
It is known that during early papermaking, the pulp was prepared in an aqueous suspension in vats in which the mould was immersed.
With the passage of time various machines for preparing paper pulps were made, and in addition to Hollander beaters, which operate with a periodic cycle, use is now made of continuous cycle refiners such as disk refiners or conical refiners. In the latter the pulp enters at one end and exits on the other side, passing through a rotary cone equipped with bars and a casing equipped with fixed counter-bars.
In contrast, in disk refiners, the pulp is treated by rotating disks.
A disk refiner basically consists of two/four metal disks positioned one in front of another, whose opposite surfaces have grooves in them directed towards the outside, the dimensions and shape varying according to the stage/degree of refining.
Each pair consists of one fixed disk and another disk which rotates rapidly and which may be moved away from or towards the first. The pulp is forced to pass inside the two plates.
The pulp, pushed by the action of the rotating disk and thrown outwards by the centrifugal force, passes through the gap between the grooves and is subjected to a mechanical refining action.
Generally, for the production of refiner disks a technique is used according to which the shape of the parts with the grooves is created using casting processes, or welding or mechanical machining processes such as routing.
It was found that the former two production methods applied in making conical bodies did not allow the aims to be achieved in terms of quality of the finished product, since in most cases the set of bars created with casting or assembly or welding processes was imprecise. It was also difficult to maintain the size of the bar and of the space for a predetermined period of use, and it was impossible to make extremely fine bars (even less than 1 mm thick) or to modify the angle of the bars.
The prior art production systems are also slow in the implementation and therefore the delivery processes and it is impossible to make spare parts with an extremely fine set of bars for any type of refiner on the market, even those with a narrow angle (older ones) which may be used to produce very particular papers which currently require modern refiners.